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Targeting antiretroviral therapy (ART) to male-male couples that are serodiscordant (one partner is HIV-infected and one is uninfected), could be an especially productive treatment and prevention strategy, say researchers from Emory University and the Centers for Disease Control and Prevention (CDC).

Eli Rosenberg, PhD, assistant professor of epidemiology at Emory's Rollins School of Public Health, presented study findings on Feb. 25 at the Conference on Retroviruses and Opportunistic Infections (CROI) in Seattle, Wash.

Using detailed data on behaviors and viral suppression of HIV-infected persons in the United States from three national HIV surveillance systems, the researchers developed a model to estimate the number of HIV transmissions in 2009 from HIV-infected MSM (men who have sex with men) to uninfected male sexual partners. The partners were categorized as main partnerships vs. casual partners.

The researchers estimated there were more than 1.3 million serodiscordant male-male partnerships that involved anal intercourse in the United States in 2009, involving 652,300 HIV-infected MSM who had 4,553,065 partners. Within these partnerships, there were 26,400 transmissions to 1,281,821 HIV-negative or unknown status anal intercourse partners.

Overall, 76 percent of transmissions were in main partnerships. Also, 70 percent of all transmissions were in main partnerships in which the infected partner was not receiving ART, even though they represented only 8 percent of serodiscordant partnerships. In contrast, casual serodiscordant partnerships of MSM not receiving ART represented 23 percent of transmissions and 79 percent of serodiscordant partnerships.

"Because there is a defined, and relatively small, number of partnerships involving risk of HIV transmission, targeting these serodiscordant relationships for ART and PrEP (pre-exposure prophylaxis) could yield a particularly high prevention result," says Rosenberg.

"To reduce HIV incidence among MSM, we should focus efforts on increasing the percentage of HIV-infected MSM on ART and the percentage of uninfected MSM in discordant relationships who receive PrEP."